Relative insignificance of mineral grain zeta potential to colloid transport in geochemically heterogeneous porous media

The role of zeta-(zeta)potential of mineral grains in the initial deposition kinetics of colloidal particles in geochemically heterogeneous porous media is investigated. Colloid deposition experiments with colloidal silica particles flowing through columns packed with chemically heterogeneous sand were carried out. Patchwise chemical heterogeneity was introduced to the granular porous medium by modifying the surface chemistry of a fraction of the quartz sand grains via reaction with aminosilane. Experimental initial colloid deposition rates and resulting collision efficiencies were compared to theoretical predictions based on the measured average zeta-potential of the chemically heterogeneous sand. It is shown that colloid deposition kinetics are controlled by the degree of patchwise chemical heterogeneity and that use of the measured zeta-potential of the granular porous medium in theoretical predictions leads to erroneous results.